I_OSC raised unexpectedly during Wake Up mode

LltWc · ‎2025-01-24

I've been implementing Wake Up mode with inductive wakeup on the ST25R3916 with custom firmware. It's all functioning as expected, except for the oscillator interrupt.

As seen in the logs below, when I switch to Wake Up mode, I mask every IRQ except I_WAM and I_WPH. Just to be safe, I added a readout. The Wake Up timer is configured to take a measurement every 100ms. But every 100ms, it sends an I_OSC interrupt when it switches to Ready to take amplitude and phase measurements. Why would this occur? Is there something beyond just M_OSC being set that I need to do?

Brian TIDAL · ‎2025-01-24

Hi,

as explained in §4.2.5 Wake-up mode of the ST25R3916 datasheet, the reader field is activated for an extremely short time to allow phase or amplitude measurements during wake-up mode. Thus, the oscillator is enabled during this short time and I_osc is triggered when the oscillator is stable.

This is a normal behavior.

Rgds

BT

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LltWc · ‎2025-01-27

Hi Brian, yes, I am aware that the oscillator is enabled in order to take inductive measurements. Why is the interrupt still being raised when I have the mask set?

Brian TIDAL · ‎2025-01-27

Hi,

see §4.3.1:

"If an interrupt from a certain source is not required it can be disabled by setting the
corresponding bit in the Mask interrupt registers. In case of masking a certain interrupt
source the IRQ line is not set high, but the interrupt status bit is still set in IRQ status
registers."

Rgds

BT

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LltWc · ‎2025-01-27

Yes, thank you, I'm aware that the bit will still be set. The IRQ readout in the log I posted only occurs when the IRQ line is set high, every 100ms, and you can see that the only bit set is the I_OSC bit. I don't see any way to interpret the behavior except that I_OSC is ignoring that it is masked.

Brian TIDAL · ‎2025-01-27

Hi,

can you connect a logic analyzer on SPI (CLK, MISO, MOSI and CS) + IRQ Line and send us the raw trace file?

Rgds

BT

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Ulysses HERNIOSUS · ‎2025-01-27

Hi,

we are using it in WU mode a lot and I_osc is not triggering the INT line when masked (M_osc=1).

I am suspecting something on the SPI/INT line we are not seeing in your logs. Please provide a logic analyzer trace.

BR, Ulysses